Processes for dewaxing petroleum distillates have been known for a long time. Dewaxing is, as is well known, required when highly paraffinic oils are to be used in products which need to remain mobile at low temperatures e.g., lubricating oils, heating oils, jet fuels. The higher molecular weight straight chain normal and slightly branched paraffins which are present in oils of this kind are waxes which are the cause of high pour points in the oils and if adequately low pour points are to be obtained, these waxes must be wholly or partly removed. Catalytic dewaxing processes are employed to selectively crack the longer chain n-paraffins to produce lower molecular weight products which may be removed by distillation. Processes of this kind are described in The Oil and Gas Journal, Jan. 6, 1974, pages 69-73 and U.S. Pat. No. 3,668,113.
In order to obtain the desired selectivity, the catalyst is usually a zeolite having a pore size which admits the straight chain n-paraffins or slightly branched paraffins but which excludes more highly branched material, cycloaliphatics and aromatics. Zeolites such as ZSM-5, ZSM-11, ZSM-12, ZSM-23, and ZSM-35 have been proposed for this purpose. Medium pore zeolites have the preferred property of selectivity and their use forms the basis of the Mobil Distillate Dewaxing process (MDDW). MDDW is a fixed bed process that typically operates at 20 to 55 atm (2058 kPa to 5660 kPa), 260.degree.-430.degree. C. reactor temperature, and 40-70 m.sup.3 /b of hydrogen circulation.
U.S. Pat. No. 4,332,670 to Antal discloses catalytic dewaxing of FCC light oil with ZSM-5 employing hydrogen recycle. U. S. Pat. No. 4,483,760 to Tabak describes sequential fixed bed dewaxing of middle distillate with flash separation. U. S. Pat. No. 4,419,220 to Lapiere et al. discloses fluidized bed dewaxing-isomerization of distillate fuel oil over zeolite beta. U.S. Pat. No. 4,541,919, also to Lapiere et al., discloses fluidized bed hydrodewaxing with ZSM-5. U.S. Pat. No. 3,891,540 to Demmel et al. discloses a combined process for catalytic cracking and distillate dewaxing using ZSM-5 catalyst. U.S. Pat. Nos. 4,181,598 to Gilespie et al 4,283,271 and 4,283,272 to Garwood et also describe the Mobil Lube and Distillate Dewaxing Process (MLDW) using zeolite catalyst. The foregoing patents, of common assignee, are incorporated herein by reference in their entirety.
Conversion of olefins to gasoline and/or distillate product is disclosed in U.S. Pat. Nos. 3,960,978 and 4,021,502 (Givens,Plank and Rosinski) wherein gaseous olefins in the range of ethylene to pentene, either alone or in admixture with paraffins, are converted into a gasoline blending stock by contacting the olefins with a catalyst bed made up of ZSM-5 or related zeolite. In U.S. Pat. Nos. 4,150,062 and 4,227,992 Garwood et al discloses the operating conditions for the Mobil Olefin to Gasoline/Distillate (MOGD) process for selective conversion of C.sub.3 + olefins. A fluidized bed process for converting ethene-containing light olefinic streams, sometimes referred to as the Mobil Olefin to Gasoline (MOG) process is described by Avidan et al in U.S. patent application 006,407, filed 23 Jan. 1987. The phenomena of shape-selective polymerization are discussed by Garwood in ACS Symposium Series No. 218, Intrazeolite Chemistry, "Conversion of C.sub.2 -C.sub.10 to Higher Olefins over Synthetic Zeolite ZSM-5", 1983 American Chemical Society.
In the process for catalytic conversion of olefins to heavier hydrocarbons by catalytic oligomerization using an acid crystalline metallosilicate zeolite, such as ZSM-5 or related shape selective catalyst, process conditions can be varied to favor the formation of either gasoline or distillate range products. In the gasoline operating mode ethylene and the other lower olefins are catalytically oligomerized at elevated temperature and moderate pressure. Under these conditions ethylene conversion rate is greatly increased and lower olefin oligomerization is nearly complete to produce a gasoline blending stock in good yield.
The olefins contained in an FCC gas plant are an advantageous feed for oligomerization. U.S. Pat. No. 4,090,949 discloses upgrading olefinic gasoline by conversion in the presence of carbon hydrogen-contributing fragments including olefins and a zeolite catalyst and where the contributing olefins may be obtained from a gas plant. U.S. Pat. Nos. 4,471,147 and 4,504,691 disclose an oligomerization process using an olefinic feedstock derived from FCC effluent. In these two latter patents the first step involves prefractionating the olefinic feedstock to obtain a gaseous stream rich in ethylene and a liquid stream containing C.sub.3 + olefin.
The conventional MOG process design is concerned with converting ethylene in a fuel gas stream, such as an FCC offgas, to gasoline. Motor octane of the gasoline produced is generally about 80-85. Typically, paraffins conversion under MOG process conditions is not significant.
It is an object of the present invention to provide a process for the simultaneous dewaxing of distillate fuel oil and the oligomerization of light olefins to C.sub.5 + gasoline.
Another object of the invention is to provide the foregoing process employing zeolite catalyst in a common conversion zone.
Yet another object of the invention is to integrate the foregoing process invention with catalytic or thermal cracking operations in order to utilize light olefin products and unsaturated gas plant separation vessels.